1. Field of the Invention
The present invention relates to an optical transmitting/receiving module to be used in optical fiber communication and to a method for manufacturing the same.
2. Description of the Related Art
In recent years, attention has been focused on optical fiber communication, by which an information of large capacity can be transmitted at high speed and with low loss and which uses optical fiber instead of metallic cable. With the progress of technique, there are now strong demands on optical devices, which can be produced at lower cost and are provided with high functions for high-speed transmission. For instance, efforts have now been made to develop an optical communication system, by which optical bidirectional transmission in outgoing and incoming directions with different wavelengths of xcex1 and xcex2 can be achieved using a single optical fiber. To produce an optical module of this type, it is necessary to use a technique to separate the wavelength of a light emitting element from that of a light receiving element and to integrate components with optical multiplexing function.
Description will be given below on a typical example of a conventional type optical bidirectional module. In the past, a structure combining an optical waveguide with a wavelength division multiplexing (WDM) filter has been commonly used to separate a signal of receiving wavelength xcex1 from a signal of transmitting wavelength xcex2. FIG. 11 shows a conventional structure of a WDM optical bidirectional module using optical waveguide disclosed in JP-A-11-68705. On a Si substrate 103, optical waveguides 102 (102a, 102b, 102c) are formed in star-like arrangement with a WDM filter 107 at the center. To an end of each of the optical waveguides 102a, 102b and 102c, a light emitting element 105, a light receiving element 106, and an optical fiber 101 are aligned by 2-dimensional high-accuracy alignment to achieve optical coupling of incident light with exit light. The alignment of the light emitting element 105 and the light receiving element 106 is generally performed by using alignment markers, which are formed in advance with high accuracy on the Si substrate 103.
An output light with the wavelength of xcex2 of the light emitting element 105 is transmitted via the optical waveguide 102a and is reflected by the WDM filter 107. Then, it passes through the optical waveguide 102c and is guided into the optical fiber 101. For the purpose of achieving optical coupling of end surfaces of the core of the optical fiber 101 and the optical waveguide 102c, a V-shaped groove fabricated with high accuracy is formed on the Si substrate 103 with respect to the position of the optical waveguide 102. Then, the optical fiber 101 is aligned along the V-groove and fixed. On the other hand, a light signal with the wavelength of xcex1 transmitted from the optical fiber 101 is transmitted via the optical waveguide 102c and passes through the WDM filter 107, and it is received by the light receiving element 106 via the optical waveguide 102b. The light receiving element 106 is designed to have such a structure that it can receive the light when the light enters from lateral side of the chip.
The conventional module as described above have the following problems: The conventional module has the optical waveguide 102, and it requires complicated process not only to form the V-groove and the alignment markers 108 on the Si substrate 103 but also to provide the optical waveguide 102 with high accuracy. Further, the optical wave guides 102a, 102b and 102c are formed in star-like arrangement with the WDM filter 107 at the center. This means that the Si substrate 103 must have larger size, and it is difficult to produce the Si substrate 103 at low cost. Also, it is difficult to produce the module in small size.
The light receiving element 106 has such a structure that the light from the optical waveguide 102b enters side surface of the element of the chip. The optical waveguide 102b must be aligned with the light receiving element 106 with high accuracy in the order of 1 to 2 xcexcm. In order to efficiently arrange the light receiving element 106 and the light emitting element 105 on the Si substrate 103, it is necessary to use high-temperature soldering reflow process. For this purpose, a resin having high heat-resistant property should be adopted for fixing optical components. Also, it is necessary to design the module with expensive ferrule to achieve reflow arrangement.
To solve the above problems in the conventional type module, it is an object of the present invention to provide a small size and inexpensive optical transmitting/receiving module without the need to use optical waveguide, which requires complicated process and larger area.
Also, it is another object of the present invention to provide a method for manufacturing an optical transmitting/receiving module, which can be produced by simplified manufacturing process.
To attain the above object, the optical transmitting/receiving module of the present invention comprises a substrate where there are provided a V-groove running in linear direction and a groove crossing said V-groove obliquely at an end of the V-groove, an optical fiber core is arranged to the end of said V-groove, a wavelength selective filter or a half-mirror is provided in said groove, and a light emitting element and a light receiving element are arranged respectively in transmitting direction and reflecting direction of the wavelength selective filter or the half-mirror.
By the above arrangement, it is possible to provide a small and inexpensive wavelength multiplexing optical transmitting/receiving module or a one-wavelength optical transmitting/receiving module without the need to use optical waveguide, which requires complicated manufacturing procedure.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein a side surface of said groove runs in vertical direction, and said light receiving element is designed as end surface incident type.
By this arrangement, it is possible to improve optical coupling of the light receiving element and the optical fiber.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein a side surface of said groove runs in oblique direction, and a second wavelength selective filter to shut off only wavelength of said light emitting element is arranged between said light receiving element and said wavelength selective filter.
By the arrangement as described above, it is possible to reduce light leakage of the light receiving element from the light emitting element. Also, the light receiving element, not of waveguide type but of front surface or rear surface incident type, can be used.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein a light reflection surface of said wavelength selective filter or the half-mirror is fixed on side surface of the groove positioned opposite to the end surface of the optical fiber core.
By this arrangement, it is possible to accurately define the position of the wavelength selective filter or the half-mirror and to improve optical coupling efficiency to the light receiving element. Also, it is possible to increase width of the vertical groove or the oblique groove to a width greater than the thickness of the filter or the like, and this makes the insertion of the filter and the like much easier.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein a light reflection surface of said wavelength selective filter or the half-mirror is brought into contact with and fixed on the side surface of said groove positioned opposite to the end surface of the optical fiber core.
By the arrangement as described above, it is possible to accurately define the position of the reflection surface without being influenced by variation in the thickness of the wavelength selective filter or the half-mirror, and to improve optical coupling efficiency to the light receiving element.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein the end surface of the optical fiber is formed in oblique direction so that it runs approximately in parallel to the surface of the wavelength selective fiber or the half-mirror.
By the above arrangement, it is possible to minimize the distance between the end surface of the optical fiber and the filter and to improve optical coupling efficiency.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein the surface of said light emitting element positioned opposite to said wavelength selective filter or the half-mirror is designed to run in oblique direction.
By this arrangement, it is possible to improve optical coupling efficiency of the light emitting element.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein the surface of the light emitting element where an active layer is not exposed to outside is formed in oblique direction.
By this arrangement, the light emitting element can be brought closer to the filter and the like, and optical coupling efficiency can be improved.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein the active layer of said light emitting element is displaced in a direction perpendicular to the optical axis, and said light emitting element is arranged in such position that the distance between said active layer and said wavelength selective filter or the half-mirror will be shorter.
By this arrangement, it is possible to improve optical coupling efficiency of the light emitting element without the need to fabricate the light emitting element in oblique direction.
According to another aspect of the present invention, an optical transmitting/receiving module as described above is provided, wherein the surface of said light receiving element positioned opposite to the wavelength selective filter or the half-mirror is formed in oblique direction.
By this arrangement, it is possible to improve optical coupling efficiency of the light receiving element.
The present invention provides a method for manufacturing an optical transmitting/receiving module, which comprises a substrate where there are provided a V-groove running in linear direction and a groove crossing said V-groove obliquely at an end of the V-groove, an optical fiber core is arranged to the end of said V-groove, a wavelength selective filter or a half-mirror is provided in said groove, and a light emitting element and a light receiving element are arranged respectively in transmitting direction and reflecting direction of the wavelength selective filter or the half-mirror, said method comprising the steps of:
inserting said wavelength selective filter or said half-mirror into said groove and fixing; and
positioning the end surface of said optical fiber core and said filter or the half-mirror by advancing the forward end of the optical fiber core along said V-groove until it reaches the filter or the half-mirror.
By this method, it is possible to perform alignment of the wavelength selective filter or the half-mirror accurately by utilizing the process to fix the optical fiber.
Also, the present invention provides a method for manufacturing the optical transmitting/receiving module as described above, said method comprising the steps of:
applying a resin having refractive index equal to that of the optical fiber to the end surface of the optical fiber;
temporarily fixing the end surface of the optical fiber to the wavelength selective filter or the half-mirror by utilizing adhesive strength of said resin not yet hardened; and
hardening said resin and fixing it to the end surface of the optical fiber positioned in said V-groove.
By this method, it is possible to fix the wavelength selective filter or the half-mirror between the optical fiber and the vertical groove or the oblique groove accurately and easily even when the wavelength selective filter or the half-mirror is in small size. Also, it is possible to produce the filter and other components at lower cost because these are in smaller size.
Also, the present invention provides a method for manufacturing the optical transmitting/receiving module as described above, said method comprising the steps of:
advancing the end surface of said optical fiber core along said V-groove until an edge of the end surface reaches the side surface of said groove; and
advancing said wavelength selective filter or said half-mirror along said groove until its tip reaches the end surface of the optical fiber core, and aligning the position of the optical fiber core with that of the wavelength selective filter or the half-mirror.
By this method, it is possible to shorten the distance between the fiber end and the light emitting element and to improve optical coupling efficiency of the light emitting element.
According to another aspect of the present invention, it is designed in such manner that wherein said optical fiber and said wavelength selective filter or the half-mirror are fixed at the same time by filling a resin having refractive index equal to that of the optical fiber into optical path near the end of the optical fiber and hardening said resin.
By this arrangement, it is possible to reduce reflection loss between the optical fiber and the air layer.
According to still another aspect of the present invention, the invention provides an optical transmitting/receiving module as described above, wherein said substrate is made of a semiconductor material, and said V-groove and the groove are formed at the same time by anisotropic wet etching process or by dry etching process, or formed at the same time by using a dicing saw.
By this method, it is possible to form the vertical groove or the oblique groove at the same time as the V-groove, and it is possible to form these grooves much easier.